ANALYSIS OF INTERACTION BETWEEN TGF AND THE MYOGENIC RESPONSE IN RENAL BLOOD-FLOW AUTOREGULATION

The present study investigates the interaction between the tubuloglomerular feedback (TGF) response and the myogenic mechanism by use of a mathematical model. The two control mechanisms are implemented in a spatially distributed model of the rat renal juxtamedullary afferent arteriole. The model of the afferent arteriole is based on in vivo measurements of the stress-strain relation in muscle strips. Analysis of experimental data shows that the myogenic response can be modeled by a linear relation between the transmural pressure and the level of activation of the vascular smooth muscle cells. The contribution of TGF to smooth muscle activity is assumed to be a linear function of the glomerular capillary pressure. The results show that the myogenic response plays an important role in renal blood flow autoregulation. Without a myogenic response, mechanisms such as TGF that are localized in the distal segments of the microvasculature would not be able to achieve autoregulation because of passive, pressure-mediated effects in the upstream vascular segments. In addition, it is shown that a strong myogenic response may lead to both propagation and enhancement of vascular effects mediated through mechanisms located in the distal part of the afferent arteriole. An ascending myogenic response could enhance the regulatory efficiency of the TGF mechanism by increasing the open-loop gain of the system. However, such a synergistic interaction will only be observed when the two mechanisms operate on more or less separate segments of the afferent arteriole. In the case where they operate on common segments of the arteriole, the outcome of the interaction may well be antagonistic.